For those trying to get VPN working with DD-WRT on iOS 5.01 this is the solution that I finally found to make it work (credit to http://cnedelcu.blogspot.com/2011/10/pptp-server-fix-for-ios-problems.html and users in this thread)
My start up script is:
echo "nopcomp" >> /tmp/pptpd/options.pptpd
echo "noaccomp" >> /tmp/pptpd/options.pptpd
echo "mtu 1400" >> /tmp/pptpd/options.pptpd
echo "mru 1400" >> /tmp/pptpd/options.pptpd
echo "default-asyncmap" >> /tmp/pptpd/options.pptpd
kill `ps | grep pptp | cut -d ' ' -f 1`
pptpd -c /tmp/pptpd/pptpd.conf -o /tmp/pptpd/options.pptpd
I then had to issue the following commands via telnet to get DNS to work:
nvram set pptpd_dns1=192.168.0.1
nvram set pptpd_wins1=192.168.0.1
where 192.168.0.1 is the DNS server address.
Finally for some reason I needed to delete and recreate the settings on the ipad/iphone instead of just modifying them before they would work. All setting are pretty standard except I have to set Encryption Level to Maximum and Send All Traffic to ON before it works properly.
I hope this helps someone